Sims autonomous choice in music...

Actual reason? The code for autonomously turning on music was developed long before musical preferences were added to the game. The devs probably just decided it wasn't worth the bother to modify the code.

If you want a psychological narrative reason . . . maybe they're punishing themselves for giving their neighbors icky fruitcake?

The autonomy in this game often doesn't make sense. I have a sim who hates dancing and almost all genres of music. So what does he do the moment I leave him alone and shift the focus on another sim? That's right, he turns on the radio and starts dancing. *facepalm*

Maybe we're the ones who chose their favorite music type, erroneously? After all, Sims are people, too. LOL Totally written with tongue firmly in cheek.